The present invention generally relates to an electrical resonator and more particularly, to a piezoelectric resonator with an improved spurious characteristic.
Conventionally, as shown in FIGS. 1 and 2, there has been available a piezoelectric ceramic resonator 4 which includes a piezoelectric substrate 1 of a quadrilateral or rectangular configuration such as a square shape, and electrode layers 2 and 3 provided over opposite main faces of said piezoelectric substrate 1 so as to employ a vibrating mode, for example, an expansion vibrating mode by which the entire substrate is to be vibrated. Since such a resonator utilizes mechanical vibrations, unnecessary spurious vibration is also present besides the main vibration, and although various suppressing methods for suppressing such spurious vibration have been proposed, application of one method is not perfect, but it is also necessary to combine several auxiliary methods therewith for the purpose. One practice for the purpose is such that as shown in FIG. 2, notched portions such as slits 5, 6, 7 and 8 generally of the same dimensions are formed each at the central portion of the respective side edges.
FIG. 5 shows one example of a spurious characteristic diagram as obtained from the known piezoelectric resonator as described above and formed with slits 5, 6, 7 and 8, each having a width of 0.5 mm and a depth of 0.3 mm and provided at the central portion of each side edge of the resonator with dimensions of 4.3 mm in one side edge, 4.3 mm in another side edge and 0.5 mm in depth (i.e., dimensions represented as in 4.3 mm.times.4.3 mm.times.0.5 mm hereinafter).